A wind turbine is a machine that converts the kinetic energy from the wind, into mechanical energy. Such mechanical energy when captured by a wind turbine may be employed to drive machinery using the abundantly available wind. Generally, if the captured mechanical energy is employed directly to drive machinery such as a pump, the device is called a windmill and if the mechanical energy is employed to drive a generator or alternator the device is called a wind turbine.
The most familiar wind turbines to the general public are windmills which are essentially horizontal-axis wind turbines which have the main rotor shaft engaged to blades which are situated at the distal end of a large and tall tower. The blades are engaged to the rotor at a substantially perpendicular angle and in order to spin the rotor the blades must be pointed in a direction into the wind. Smaller windmill type turbines are constantly redirected into the windstream by a simple wind vane. Larger windmills or horizontal axis turbines being heavier generally employ a wind sensor coupled to a motor to constantly reposition the blades to intersect the windstream driving them. Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower to avoid it. The rotor is usually engaged to a gear box which communicates the force of the turning blades to machinery such as a generator or alternator which is turned to generate electricity.
Horizontal axis style turbines have a number of disadvantages. First they have difficulty operating in the light winds near the ground and must be elevated and employ tall towers able to support the force of the wind against long blades. Such structures while appearing attractive to an engineer are generally not well received by the public who consider them an eyesore. Further because of their height and weight, horizontal axis turbines are difficult to install and maintain.
Vertical axis wind turbines on the other hand, have the main rotor shaft running vertically. This arrangement has a key advantage over the horizontal axis turbine in that the generator and/or gearbox can be placed at the bottom, near the ground so the tower doesn't need to support it. Further, vertical axis turbines do not require the very large blades and tall tower to support them and the blades do not need to be constantly repositioned to point into the wind.
Power for vertical-axis wind turbines is generally provided by wind acting against the plurality of wing-shaped blades and the lift created by the wind passing over the surfaces thereof. One surface being longer than the other will create a lifting force as the wind traverses and accelerates to reach the rear of the blade at the same time as the wind traveling over the shorter surface. The lift created is perpendicular to the direction of the wind and therefore it is advantageous to reposition each blade to maximize lift during traverse through the airstream and minimize drag when rotated out of a perpendicular encounter with the same airstream.
Current drawbacks to vertical axis wind turbines are caused by the fact that the torque developed by the multiple blades usually pulsates in strength due to the combination of wind force on some blades and drag created when other blades rotate into the wind. It is also difficult to mount vertical-axis turbines on tall towers meaning they must operate in the often slower and more turbulent air flow near the ground. Under current designs for such vertical axis turbines these considerations can result in a much lower energy extraction efficiency.
However, since they operate closer to the ground and are simpler to assemble and install, vertical axis wind turbines are much easier to employ on a small scale to power homes and small businesses. Additionally, they do not present the large eyesore that conventional horizontal axis wind turbines exhibit. Finally, vertical axis wind turbines are much safer for wildlife such as birds which frequently fall prey to the large rotating blades of horizontal axis wind turbines since the low-positioned smaller blades are not encountered by unsuspecting wildlife in flight.
As such there is an unmet need for au improved design for a vertical axis wind turbine to allow wider employment of such devices to produce energy. Such an improved design should overcome the drawbacks of conventional devices by minimizing the torque fluctuation as the vanes circle the axis. Such an improved design should maximize the power captured from the winds blowing low to the ground. Further, such a device should provide a sheltered mechanism to prevent the deleterious effects of weather exposure and to provide convenient access for surfacing from the ground from below the turbine body.
In this respect, before explaining at least one embodiment of the invention in detail it is to be understood that the invention is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for designing other vertical-axis wind turbines and methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention.
An object of this invention is the provision of a vertical-axis wind turbine that optimizes blade positioning relative to the windstream to maximize torque.
A further object of this invention is continual optimization of each blade angle relative to oncoming wind, to maximize the force generated by lift on the respective blades at each position during their rotation around an axis.
An additional object of this invention is the provision of such a vertical-axis wind turbine which employs an airfoil pitch control enabling operation efficiently in light winds.
It is a further object of the invention herein, to provide such a vertical-axis wind turbine which employs operating mechanisms deployed below the rotating airfoils for easy access and housed in a fashion to shield the operating mechanisms from the elements.
These together with other objects and advantages which will become subsequently apparent reside in the details of the construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.